This invention relates to the field of hot dip molding and specifically relates to a process for making a composite dip molded article having a first part of a solid plastisol and a second integral skin of a chemically blown plastisol.
We are aware of Kelly U.S. Pat. No. 4,344,303 which discloses a laminated plastic cooling device in which a flexible insulating layer, which may be of a cellular structure, is provided with cavities filled with a freezable gel and a flexible plastic liner is attached by adhesive bonding, heat welding or sonic welding. The foam rubber layer is described as being extruded, cast or molded in a conventional manner.
In the present invention we utilized a conventional dip molding process to form an integral article having one layer of solid plastic and an attached integral layer of foamed polymer. Conventionally, when using a hot dipping process, a heated mandrel is dipped into a plastisol so that the heat from the mandrel causes the surrounding plastisol to gel on the mandrel. The mandrel is then withdrawn from the plastisol at a slow steady rate to prevent runs and drips. The mandrel with the partially gelled plastisol thereon is then post-baked in a forced air oven or in a bath of molten salt or other noncompatible oils to fuse the plastisol. After a predetermined time the mandrel is taken out of the post-bake medium and either air cooled or water cooled after which the plastisol part is stripped from the mandrel.
The foregoing process is very satisfactory for a solid polymer part but when this process is utilized with a chemically blown plastisol foam, the finished part is unacceptable from an esthetic and functional standpoint. A part made in this fashion from a chemically blown plastisol has craters and blister marks on the inside, that is, the side touching the mold, and similar defects on the outside surface. These defects are caused by excess heating or uneven heating caused by the foam development, dirty mandrel, etc., and is not a commercially feasible process. In addition, a part made this way is very flimsy and soft and has very little "body".
Accordingly, one of the principal objects of the present invention is to provide a process for making an integral article by a hot dipping process, which article has a solid plastic layer and a foamed plastic skin.
A further object is to provide a process of dip molding using two types of plastisol, the first of which is a solid type and the second of which is a physically blown foam type. It is still another object to provide an integral plastisol object having a solid layer and a chemically bonded foamed skin. These and other objects and advantages will become apparent hereinafter.
The present invention comprises a process for hot dip molding in which the mandrel is heated, dipped into a solid plastisol, and while still hot the plastisol covered mandrel is dipped into a second compatible plastisol which contains a chemical blowing agent and the resultant product is fused and foamed to form an integral object having a solid polymer layer and a foamed polymer layer.